Biosensors are used to detect the presence and/or levels of biomolecules, typically in a fluid sample. For instance, biosensors may be used to determine the levels of particular chemicals in biological fluids, such as blood. Specific sensors can therefore be used to determine the levels of glucose, potassium, calcium, carbon dioxide, and other substances in blood samples.
Biosensors such as these often use an electrochemical system to detect a particular substance of interest. The electrochemical system includes substances such as enzymes and redox mediators to react with the substance of interest (the target substance) and to thereby produce ions that can carry a current. A set of electrodes are used to generate an electrical potential that attracts the ions to the electrodes, creating a circuit that can be used to measure the resulting current.
In one type of system, a biosensor includes an enzyme which is immobilized by a membrane. The target substance in a fluid sample migrates through the membrane and reacts with the enzyme. This forms ions within the fluid sample. These ions then migrate through the fluid sample to the system's electrodes. The migration of the ions to the electrodes generates an electrical current that is measured. Because the current depends upon the concentration of the target substance in the sample, the measured current is then translated to a concentration of the target substance.
There are a number of problems with these conventional biosensors. For example, they are relatively slow. This is, at least in part, a result of the fact that it is necessary in electrochemical biosensors to allow a certain amount of time to pass before the current resulting from the ionization of the target substance in the sample is established. Only after this current is allowed to establish itself can it be measured to provide a reasonably accurate estimate of the concentration of the target substance.
Even after the current resulting from the ionization of the target substance is established and measured, the resulting estimation of the target substance concentration typically is not as accurate as would be desirable. This is a result, at least in part, of the fact that the sample being tested typically contains various other substances, some of which may interfere in the process. For instance, some of these other substances may ionize in the sample and thereby increase the measured current, leading to an overestimation of the target substance concentration. Alternatively, some chemicals may react with the ions of the target substance, thereby reducing the measured current and causing an underestimation of the target substance concentration.
It would therefore be desirable to provide systems and methods that enable the testing of samples to determine the presence of target substances more quickly and more accurately than is typically possible using prior art systems and methods.
While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiments which are described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.